The present invention relates to a bi-directional flow sensor used to measure flow rate of a fluid flow. More particularly, the present invention relates to a differential pressure flow sensor of the type using a flow restriction member to produce a pressure drop within the fluid flow, a measurement of which can be used to establish the direction and flow rate of a fluid flow.
Fluid flow sensors can be used in many different applications, such as in industrial process control environments, to measure flow rates of process fluids (liquids and gases) and provide flow signals for flow indicators, controls, and flow volume metering. Differential pressure flow sensors measure the fluid flow rate in a pipe or conduit by measuring a pressure drop across a discontinuity within the pipe. One way to form the discontinuity is to place a flow restriction member or primary element within the pipe to produce the desired pressure drop. One such flow restriction member is an orifice plate that restricts the fluid flow and produces the measured pressure drop. An example of an orifice plate is the orifice restriction used in Model 1195 Integral Orifice produced by Rosemount, Inc. of Eden Prairie, Minn. These flow restriction members are generally uni-directional allowing for flow rate measurements of fluid flows moving in a single direction.
Typical flow rate measuring systems tap the pipe containing the fluid flow on either side of the flow restriction member and measure the pressure at each tap and use an external pressure sensor to obtain the pressure drop. Impulse or gauge lines filled with fluid communicate the pressure at each tap to the external pressure sensor. Such systems have relatively high installation costs due to the need to attach an external pressure sensor to the pipe, and to provide leakage protection at the locations where the pipe is tapped. Additionally, impulse lines attenuate the pressure signals and introduce delays thereby reducing the sensitivity and responsiveness of the flow measurement. Also, in gas applications, condensing gases in the impulse lines can cause erroneous readings. Furthermore, the use of impulse lines can also render these types of flow measuring systems sensitive to their position. As a result, they must be recalibrated each time their position changes.
A bi-directional differential pressure flow sensor is provided that is configured to establish a direction and flow rate of a fluid flow. The flow sensor includes a flow restriction member, a differential pressure sensor, and processing electronics. The flow restriction member is configured to produce a pressure drop when placed inline with the fluid flow. The differential pressure sensor is embedded or integral with the flow restriction member and produces a differential pressure signal that is indicative of the pressure drop. The processing electronics produces a flow rate signal that is indicative of the direction and flow rate of the fluid flow as a function of the differential pressure signal.